This invention concerns an apparatus and method for making composite products, including board products, that includes applying a hot, dry gas to filler and thermoactive materials, particularly cellulosic and thermoplastic materials, in the continuous production of the composites.
Products that combine wood materials with thermoplastic materials are known. These products generally are made using batch processes, such as processes that employ heated platens to apply heat and a compression force to the substrate, instead of continuous processes.
Recently, products comprising waste plastics and waste cellulosic materials have been developed, most of which are made by extrusion or injection-die methods. Examples of patented inventions concerning wood/plastic composite products include:
(a) Smith""s U.S. Pat. No. 3,995,980, which describes forming mixtures of materials using three separate delivery systems, and thereafter extruding products comprising the mixture;
(b) Goforth et al.""s U.S. Pat. No. 5,088,910, which describes an extrusion process for making synthetic wood products from recycled materials, such as low or high density polyethylene;
(c) Wold""s U.S. Pat. No. 5,435,954, which discusses a method for forming wood-plastic composites comprising placing mixtures of such materials in molds and subjecting the mixture to sufficient temperatures to cause the material to occupy the mold and assume its shape; and
(d) Reetz"" U.S. Pat. Nos. 5,155,146 and 5,356,278, incorporated herein by reference, which describe extrusion apparatuses and processes for processing charges that include expanded thermoplastic materials, such as polystyrene.
There are several disadvantages associated with the inventions discussed above. A principal problem associated with extrusion and injection methods is that the particle size of the materials used to form the composite must be fairly small. Otherwise, the particle size of the composite mixture is too high to be extruded or injection molded efficiently. Moreover, extrusion and injection processes are further limited by the ratio of filler materials, such as wood, to the thermoactive materials that can be used in the charge (i.e., the mixture of filler material and thermoactive material used to form the final product). This puts undesirable constraints on the products that can be produced.
Another problem associated with these prior processes and apparatuses involving heated platens is that they produce products batchwise, instead of continuously. This substantially reduces product throughput. For example, heated platens take too long to heat composites completely throughout their cross section. If the temperature of the platens is increased too much in an effort to speed production, the composite product may burn or scorch, particularly at temperatures above about 400xc2x0 F. Moreover, many processes that use platen presses require that the platen not only be heated but also cooled during each production cycle. This decreases product throughput and is expensive in view of the energy required to complete the serial heating and cooling steps.
Steam injection processes also can be used to produce composites. However, the initial steam heating stage is followed by continued heating to remove all of the water applied to the composite during the steam injection process. The combination of heating the composite to form products, followed by continued heating to remove water, requires a longer period of time and is more expensive than is desirable in a commercial process.
German Patent No. 14 53 374 (the ""374 patent) describes a continuous process for forming composites comprising waste plastic and waste wood. A mixture of waste plastic and waste wood is pressed in the nip between two rollers and hot air is applied to the substrate as it travels around the rollers. The structural features of the apparatus described in the ""374 patent are limiting. For example, the ""374 patent teaches applying hot gas to only one of the two major opposed surfaces of a substrate at a time. As the substrate passes over one roller gas is applied to one surface, then as the substrate passes over a second roller, hot gas is applied to the opposite surface. There is considerable energy loss, and therefore added expense, as a result of heated gas being vented to the atmosphere after passing through the composite. This also may present a health problem in that vented gas may include volatile organic compounds (VOCs) that present a health risk.
Furthermore, by following the radius of the rollers, the outside surface of the mat is stretched relative to the inside surface. This causes fissures on the outside surface. Such fissures are undesirable when manufacturing a thick product in combination with an outside surface comprised of a fines material (i.e., an outside surface comprised of small particles).
Despite the inventions discussed above, there still is a need for an effective and efficient apparatus and method for continuously forming composite products.
The present invention overcomes the difficulties of the prior art by providing an effective and efficient composite consolidation apparatus and method for continuously forming composite products comprising filler materials and thermoactive materials. The apparatus and method are particularly suited for forming composites comprising waste cellulosic materials and waste thermoplastics.
One embodiment of the consolidation apparatus includes a hot-gas distribution system having at least one pair of gas cells, more typically plural paired gas cells, such as rollers or hoods, for applying hot air to the charge. A first cell of each pair applies gas to the charge, and generally is referred to as an application roller. The second cell of each pair, referred to as a suction roller, operates at a pressure less than the application roller, i.e., a pressure differential exists between the application roller and the suction roller. Certain embodiments of the apparatus include at least one set of baffles positioned adjacent a cell, at least one shroud positioned about a cell, or at least one set of baffles positioned adjacent a first cell and at least one shroud positioned about a second cell to eliminate or substantially reduce the amount of gas that is vented to the surrounding atmosphere.
The consolidation apparatus can be used in combination with other apparatuses to form a system. One embodiment of the system comprises: (1) a mixer, such as a cyclone, for continuous or batchwise formation of mixtures of filler material and thermoactive material; (2) optionally a prepress for optional densification of the mixture prior to subsequent treatment; (3) a consolidation apparatus having a thermal consolidation zone, and perhaps a densifying zone, for continuously applying hot-gas to a moving charge, the zone having at least one pair of and perhaps plural paired gas cells wherein a first cell of each pair applies gas to the moving charge and wherein a second cell of each pair operates at a pressure less than in the first cell; and (4) a mechanical densifying apparatus for applying a densifying pressure to the charge downstream of the consolidation zone. The system may further include a mat-forming apparatus downstream of the mixer and upstream of the consolidation zone.
The invention further comprises a method for continuously forming composites. A mixture is formed comprising a waste thermoactive material and a waste filler material. The mixture is then continuously consolidated by applying a hot, dry noncondensable gas to the mixture. The apparatus described above may be used to continuously apply the gas to the mixture, and the mixture may move continuously through a zone where the consolidating gas is applied. Generally, but not necessarily, the filler material comprises cellulosic material, and the thermoactive material is a thermoplastic material. The mixture may further include materials selected from the group consisting of biocides, fungicides, fire retardants, conductive materials, pigments, water retardants, wax-like materials, coupling agents, crosslinking agents, and combinations thereof.
Still another embodiment of the present invention comprises a method for forming a product from cellulosic material and thermoactive material. The method comprises first providing a mixture comprising a predetermined amount of cellulosic material and a predetermined amount of thermoplastic material. A mat is formed from the mixture, and the mat is then consolidated. The consolidated mat is pressed to a predetermined final product thickness. At least a portion of a surface of the mat or product is then surface modified. Consolidating the mixture into a mat can include forming a first face layer of the face mixture, forming a core layer of the core layer mixture on the first face layer, and forming a second face layer of the face layer mixture on the core layer. Forming the core layer may include depositing mixtures of wood flakes and plastic flakes according to mixture flake size in successive layers such that the core layer has larger flakes adjacent the first face layer and adjacent the second face layer, and smaller flakes between the larger flakes in a middle portion of the core layer. The method also can include fusing a sheet comprising a plastic material to least one major planar surface of the mat. The plastic material can then be surface modified, such as by e-beam or flame treating the material. Grafting chemicals can be applied to surface modified mats, plastic material or products.
A method for forming a product having a first face layer and a core layer also is described. The method comprises preforming a first face layer to form a preformed a first face layer. A core layer is deposited on an upper surface of the preformed first face layer.
A method for forming a face layer for a composite product also is described. The method comprises making a face layer mixture comprising predetermined amount of thermoplastic material and cellulosic material. The mixture is deposited on a forming surface, and the mixture is then heated to an activation temperature. The method can also include applying heat energy to the mixture to form a melted face layer.
A composite product also is described. The composite comprises a first portion comprising a first core formed from a mixture comprising a cellulosic material and a thermoplastic material, and at least one face layer attached to at least one major planar surface of the first core. The at least one face layer is formed from a mixture comprising a cellulosic material and a thermoplastic material. The product also comprises a second portion bonded to the first portion. The portion comprises a second core formed from a mixture comprising a cellulosic material and a thermoplastic material, and at least one face layer attached to at least one major planar surface of the second core, the at least one face layer is formed from a mixture comprising a cellulosic material and a thermoplastic material.